Cotton felt and method of making the same



Nov. 7, 1950 Filed Jan. 26, 1946 H. A. SECRIST ,528,793

COTTON FELT AND METHOD OF MAKING THE SAME 3 Sheets-Sheet 1 INV NTOR A/Mu Ally am, #iz

Nov. 7, 1950 H. A. SIECRIST 2,528,793

COTTON FELT AND METHOD 0F MAKING THE SAME Filed Jan. 26, 1946 3 Sheets-Sheet 2 Nov. 7, 1950 H. A. SECRIST COTTON FELT AND METHOD OF MAKING THE SAME Filed Jan. 26, 1946 3 Sheets-Sheet 5 Patented Nov. 7, 1950 COTTON FELT AND METHOD OF MAKING THE SAME Horace A. Secrist, Dedham, Mass, assignor to The Kendall Company, Boston, Mass., a corporation of Massachusetts Application January 26, 1946, Serial No. 643,799

14 Claims. 1

This invention concerns felted cotton fiber textile materials, and apparatus and methods of making the same. More particularly, the invention provides for the first time in the art a true felt which may be composed wholly of cotton textile fibers, and a process for producing such a felt. This felt is soft, porous, highly conformable, flexible and extensible; has adequate strength for many textile uses; and may be employed for many of the purposes for which wool felts are used. It comprises inter-curled and entangled cotton textile-length fibers having artificially-induced kinks, twists and bends.

It has long been known that cotton fibers lack the natural felting properties of wool and similar fibers. Cotton fibers do not respond to the wool felting process, that is, to mechanical manipulation in the presence of moisture and heat. Under such conditions they do not condense, tangle and interlock and do not produce a felt or a material of adequate tensile strength for textile usages.

To obtain such strength in an unwoven textile material of cotton fibers, it has heretofore been necessary to employ fiber-to-fiber bonds to lock the fibers together into a coherent body by the addition to the fiber mass of a binding agent, or, by including special binder fibers. These bonded fiber products, which are dependent upon a binding medium (mass or fiber) and adhesive bonds writhing, curling, kinking, looping, and twisting in all directions with resultant contracting,

ently to a softening of the individual fibers. By this process, however, I am able, upon removal of the treating chemical, to produce my novel product-a strong, extensible, conformable felt consisting of fibers having substantially their natural strength but arranged in a new artificially-induced curled, kinked, twisted, entangled, and interlooped condition. Moreover, the removal of the treating agent is accomplished without reducing, in fact while often increasing, the resultant contracted condition of the frictionally interlocked fiber mass, produced by the chemical action.

As the characteristic high flexibility, extensibility, and compressibility of the felt indicate, the process produces little or no loss of individual fiber identity, that is, no'material fusing together of fibers. The strength of the product, as in a wool felt, derives from the fact that the fibers have curled and kinked about each other, producing a new and extensive fiber entanglement and interlocking which greatly increase the mutual frictional engagement of the fibers and hence the tensile strength of the material. The same factors, coupled with substantially complete fiber identity and freedom, though with an overall-shortening of length due to kinking, twisting and bending, serve to explain the high extensibility and flexibility of the material. The end product is soft because the fibers are not matted down nor interfused and have a loft such as that of most wool felts.

The physical properties and structural'characteristics of the cotton felts are believed to be the result of the interaction of two factors: One, the original arrangement of the fibers of the untreated cotton brought about by such mechanical processes as carding or other means of original dry-assembly; and, two, the subsequent profound modification of the'original fiber configuration and course of the fibers by chemical treatment. It is thought that basically the ability to produce these changes'is determined by the structure of the cotton fiber itself which has as a natural pattern a helical arrangement of its ultra-structural units which are reversed in direction at regular intervals. Thus when the fiber is treated it swells, accompanied by a release of the natural set of the fiber and a release of the energy forces of the fiber. This energy release is associated with a helical twisting, and/or untwisting, of the fiber on its long axis and a three dimensional writhing which results in the appearance of major and minor kinks, regional and localized coiling, and sharp twisting and even reversal of its course. As the fibers are in intimate relation to one another, such writhing and movement of the fibers causes them to become entangled with one another. Furthermore, all such changes contribute directly to the conversion of the fibers into forms which enable them to interlock readily with one another to produce the physical pattern described above. The reaction of the fibers in intertwining and interlocking is so pronounced that when superposed layers of fibers are treated and the process is carried sufiiciently far, the constituent layers are intimately locked together to produce a continuous system.

During the treatment, the fibers assume a new and greatly entangled and interlocked relation with one another. Removal of the treating solution after the fibers have assumed their newly entangled, kinked andftwisted condition, as I have discovered, causes the fibers to become set in a new conformation and configuration, and, thereafter, the dried fibers are reluctant to assume any other configuration, and resist any forces exerted upon them tending to change their configuration. As the felted product is essentially an entangled, interlooped and frictionally interlocked mass of the individual set fibers, and as such elemental fibers resist changes in configuration, the felt itself attains thereby a high degree of resistance to forcestending to interrupt its continuity of structural coherence or to deform it from its contracted condition.

The extent of fiber curling, kinking and entanglement produced,upon which the strength, extensibility and other unique qualities of the product are dependent, corresponds closely to the extent to which the dry-assembled fiber aggregate undergoes a permanent lengthwise and widthwise contraction in the process. amount of such contraction that can be obtained is a controllable variable from as high as 95% area-contraction down to as little as 40%, with a corresponding range of products differing in the extent to which the new felt-like properties are realized.

The variable conditions or factors of the process, by which are determined andcontrolled the extent to which the desired new characteristics are imparted to the fiber aggregate, are numerous and concern not only the chemical treatment itself but also the manner in which the fiber mass is prepared for the chemical treatment and is processed following the chemical treatment.

It is preferred that the fibers be first cleaned, for example by boiling and bleaching. The initial closeness of association of the fibers has some effect on the extent of the felting action obtained. Superimposed, unpressed films of dry-assembled fibers, preferably carded or garnetted cotton fiber webs, are suitable for treatment in the process and thereby acquire the new felt-like properties to a useful extent. I have found, however, that by increasing the density of such a carded or garnetted fiber layer, by a prepressing operation, the properties of the resulting felt may be substantially altered. For example, felts made from unpr'essed webs are usuallysoft and thick and are characterized by high extensibility and permeability, While those made from heavily hot-calendered webs, under conditions of say 350 F. and

The

1800 pounds per inch of Width, are stronger, more dense, thinner, and less extensible. It has been found, however, that the most useful commercial felts are made from lightly cold-pressed webs, for example under pressure of 10 pounds to 20 pounds per inch Width. In the ensuing chemical treatment the pressed webs fluff and full as they contract, tending to increase in thickness.

The arrangement of the fibers in the body or mass thereof to be treated also has an effect on the results realized. They should be thoroughly intermingled and moreor less randomly intermixed, with a fairly even distribution between fibers arranged longitudinally and those arranged transversely of the layer for more nearly balanced longitudinal and lateral strength in the product. Furthermore, since the process depends upon writhing, kinking and looping of individual fibers thus to become mutually entangled, it is'important that the fibers have some degree of freedom of motion during the treatment and that the association of the fibers be such as to permit such motion.

Any suitable means may be employed for initially assembling the fibers but a satisfactory arrangement of fibers is obtained in carding, garnetting or the like. 7 I prefer," however, initially to form a body of several parallel superimposed sheets of the fibers which have been carded or otherwise assembled. It is a characteristic of my product, when made from multiple parallel superposed sheets, that the writhing of the fibers during treatment effects a fiber entanglement and interlocking between fibers of adjacent carded sheets so as to form a homogeneous product which has substantial resistance to delamination. Thus when carded sheets are superposed in parallel relationthe resultant body is usually stronger longitudinally than laterally, apparently because the carding produces a somewhat greater distribution of fibers arranged longitudinally than of those arranged laterally of the. sheet. On the other hand, the product obtained by cross-.- laying alternate carded sheets in forming the body is of more evenly balanced strength longitudinally and laterally, but this product has a greater tendency to delaminate under stress. For uniformity of the final product, the fiber dis-.

tribution should be fairly even throughout the body, as it is in a carded fiber sheet.

As previously stated, the preferred treating chemical of the process is an aqueous solution of caustic alkali such as sodium, potassium, or lithium hydroxide. Other ibasic cellulose swelling agents may be employed, such as solutions of sodium zincate, quaternary ammonium bases such as benzyl trimethyl ammonium hydroxide, and the like. Aqueous sodium hydroxide solution is usually employed because it is easier to work with and control, comparatively inexpens sive, and produces entirely satisfactory results. For convenience, all of said materials are herein termed causticizing agents.

' Using aqueous sodium hydroxide solutions,

satisfactory results have been obtained with solu--w tion concentrations of at least 8% and less than 30% NaOH at temperatures from just above the freezing point of the solutions to +25 C. Preferably, and for best results, such solutions are used in concentrations. of at least 10% and less than 18% NaOH at temperatures from ?10 C. to +l5 C- Other rea nts may be empl yed at corresponding effective strengths and temperatures.

The manner in which the fiber body is sub jected to the chemical treatment has a controlling effect upon the results produced. Since the felting action of the chemical on the fibers is necessarily accompanied by shrinkage of the fiber body, during the chemical treatment the body must be freed of restraints which would prevent shrinkage, such as tension and substantial surface friction. I have found that maximum effects are obtained by floating the fiber body without restraint, either longitudinal or transverse, in a bath of the treating solution. If, instead, the fiber is restrained, to any material extent, from freely contracting during thechemical treatment, felting action and shrinkage are seriously inhibited. Thus, if instead of floating freely, the sheet is held under longitudinal tension or drag, felting action and shrinkage are seriously impaired. I may, for example, provide the requisite freedom from tension of the fiber sheet while floating in the bath by overfeeding the dry-assembled sheet onto the surface of the liquid, that is, feeding the fiber sheet to the bath faster than it is withdrawn therefrom, the extent of this overfeed being at least equal to theextent of the desired longitudinal shrinkage of the sheet. Alternatively, the requisite freedom may be provided and tensile strain on the material avoided by overfeeding the sheet down an inclined trough while supporting it through the medium of underlying causticizing liquid and subjecting it to the action thereof, the weight of the liquid and of the material aiding longitudinal condensation of the moving sheet. If. the trough be formed, as isvpreferable, with a transversely curved crosssection, the transverse contraction may also be augmented by gravity, 1. e., the weight of the sheet and causticizin material.

The maximum felting, contractive effects of the sheet is positively supported throughout its area after its causticizing treatment and during its subsequent treatment for removal of the chemical, by carrying it on a moving screen, belt,

' or other suitable supporting means.

The chemical solution is washed from the shrunken fiber sheet, preferably by flowing a large quantity of water on the fiber while it is carried on a moving screen or like foraminous structure through which the liquid drains. erably, although not necessarily, the fiber is then neutralized with acid or other suitable agent, such as acetic acid or sodium bicarbonate, and again washed. The fibrous material, washed free of treating chemicals, is finally dried to complete the processing. After washing, the fiber sheet has attained sufficient strength to permit normal handling during the drying operation.

If desired, certain improvements in mechanical properties may be obtained by a wet-stretching operation. Breaking strength and modulus of elasticity may be increased by controlled stretching after the treating solution has been substantially removed. If the treated felt has a greater orientation of fiber in one direction than another, as evidenced by the greater strength or greater Pref . plan view of a typical carded mass of cotton fibers prepared for felting by causticizing according to the invention;

Fig. 2 is a photomicrograph (20w) showing" a plan view of a felt produced by causticizing,

washing and drying according to the invention knotted. In cross-section the fibers are cylin a card-ed mass of cotton fibers as illustrated in Fig. l, the layer having sustained an area shrinkage of approximately in the felting;

Fig. 3 is a photomicrograph (8032) showing a plan view of individual cotton fibers teased from the carded mass shown in Fig. 1; Fig. 4 is a photomicrograph (80a?) showing'a plan view of individual cotton fibers teased'from the felt shown in Fig. 2;

Fig. 5 is a diagrammatic side elevation view of a preferred apparatus of the invention for performing the caustici'zing, washing and drying steps of the process as a continuous operation; and

Fig. 6 is a plan view of a portion of the apparatus shown in Fig. 5.

Referring to Figs. 1 to 4 of the drawings, the cotton fibers of the Web prepared for felting (Figs. 1 and 3), in thisinstance by carding, have their usual physical structure which is essentially that of a straight, flattened tube twisted helically along its axis, as clearly appears in Fig. 3. These 'fibers are associated together by the carding operation into a more or less random criss-cross network'in which their natural form is retained and the fiber direction is mainly parallel to the surfaces of the web. Because of their straightness and smoothness, the fibers do -not tangle with one another but are loosely the fibers show regional coiling or tortuous,

corkscrew-like bends and twists. They may even twist completely backward in their course. They have the appearance of being gnarled and even the directional lay of the fibers in the carded.

W Si een in re ei Pa a t centration and mutual contact,

seam

the surfaces of the web, is substantially modified. As appears in Fig. 2', there is a tendency for the fibers to group about centers of high fiber conforming a sponge-like network of fiber clots interspersed with small voids.

Felts which have been less highly shrunken than the product shown in Figs. 2 and 4 exhibit like changes in physical structure and interrelation of the fibers but to a somewhat lesser ex-.

tent. In general, these changes are readily observable under moderate magnification.

Referring now to Figs. 5. and 6 of the accompanying drawings, which illustrate-preferred ap paratus and method for performin the chemical treatment and subsequent steps of theprocess as a continuous operation; l designates a roll, for example, of cotton fiber sheet F prepared for the causticizing treatment, preferably by superimposing carded webs of boiled and bleached cotton fiber as previously described. The sheet F is unwound from the roll [0 by being drawn between suitably driven feed rolls [2 which feed the sheet ontothe' surface of a bath of the treating chemical or caustic C maintained in a tank or trough l 4.

The sheet F floats in the caustic toward the' opposite end of the tank, shrinkin substantially both longitudinally and laterally as it proceeds. Near the far end of the tank the shrunken sheet moves over and is advanced by the underlying forwardly moving surface of a conveyor screen i6 which passesabou-t aroller I8 located in the liquid in the tank and is carried thereby at a gradual incline from the tank- The feed rolls [-2 are driven by suitable driving connections (not shown) to over-feed the sheet onto the bath, that is; tofeed the? sheet to thebath at a rate faster" than the shrunken sheet is carried therefrom by the conveyor screen I6.

The refrigerated caustic solution is continu ously supplied at a. controlled rate to the tank M: from. a: refrigerated container 20 by a feed pipe 22" at the fiber-feed end of the tank. and continuously flows from the tank by means of an outlet pipe 24 at the opposite end of the tank leading to a pump 26. which. returns: the caustic to container 20 through pipe 28.

Thusthere is provided a continuous controlled rate of flow of the caustic in the tank from the feed end toward the outlet end, which flow or. current carries: the freely floating fiber sheet to ward the conveyor H5; The caustic is discharged by feed pipe 22into aweir 36- at the feed endof the tank and flows over the lower front wall of the weir irr a stream of uniform depth extending the full width of the tank. The outlet into pipe 24 is located at the front end of tank 14, beyond the roller [8 and the portion of screen I6 passing thereover sothat the flow; of caustic is through thescreen, positively depositing the, fiber sheet thereon.

The bottom of tank 14 slopesdownward'ly' at 32 from a' point a short distance-forwardly of thepoint of feed of the sheet onto the caustic to' a point near the front end of the tank. Also, as shown in-Fig1 6; the, walls of the tank converge inwardly from a point near the point of feed toadjacent the, forward 'en'd'i of the tank. The' increase in depth of the bath' produced by the downwardly sloping bottom portion 3Zof the tank more than offsets the loss in widthdue td the converging walls of the tank, with the re sult' thattherate 'of jfibwbfthe'caustic in the I R=V W where R is'the rate of feed new the ate of .withdrawal'in unitsof length of the fiber sheet per unit of time, and P is'the maximum percent of the longitudinal shrinkage which the chemical is capabl of producing in-the fiber sheet floated therein without restraint; The value for P can be readily'determined by floating a test length of the fiber sheet in the chemical andcomparing" its'shrunken lengthito original length when the shrinking action of the chemical is'complete or has been completed tojthe extent desired. The

varied rate of flow and length of the chemical bath from the feed rolls IE to the conveyor l6 should be such as to provide sufficient time for completion of the shrinking or felting effect which is usually of the order of one-half to three minutes.

The rate of feed of the caustic to the tank and the rate of its withdrawal are adjusted so that the initial flow of thecaustic in the shallow feed end of the tank approximates in speed the rate of feed of the fiber sheet into the tank, whereas the rate of flow in the deeper front end of the tank where the caustic passesthrough the screen is considerably slower; approximating the rate of withdrawal of the fiber sheet from the caustic by the screen. The point where the tankbe'gins to deepen is approximately the point where the sheet is first thoroughly wet out by the caustic and the shrinking action commences. Thus, as the fiber sheet shrinks, the rate at which it is advanced by the fiow of caustic diminishes from approximately the rateof feed of the sheet into the caustic to approximately theIesserrate of withdrawal of the shrunken sheet from the caustic. This decelerated fiow of the caustic greatly facilitates longitudinal shrinkage of the fiber sheet, since the frictional resistance of the liquid to the longitudinal shrinking forces generated in the sheet by the kinking and curling action of the caustic on the individual fibers is thereby reduced or evencompletely eliminated Likewise, the transverse narrowing of the tank toward its forward end produces some lateral component of fiow of caustic in the bath which tends to facilitate the transverse shrinkage of thesheet.

The screen conveyor I6 passes from-the roller 18, where it receives and carries th wet, causticized and contracted fiber sheet along the upwardly inclined path to .a roller3 3, thence horizontally to a roller 36, thence. downwardly and back under rollers 38 and 4'9 and over roller 42' to roller l8. A trough 4,4 slants forwardly and upwardly from the front end of the tank under the conveyor screen to catch caustic draining from the sheet as it passes upward to the roller 34, and returns the caustic to tank I 4.

The screen, in passing from roller 34 to roller 36, carries the sheet first under two successive weir troughs 56, 48 which gently flood wash water over the surface of thesheet. This wash water drains through th sheet and conveyor screen Washing out the bulk of the caustic, and is collected in a trough 50 immediately below the screen, from which trough a drain pipe 52 may lead to a caustic recovery or concentrating apparatus (not shown). A suction box 54 at the front end of trough 50 applies suction to the sheet through the screen to complete the removal of wash waters.

After leaving the suction box 54, the sheet is carried beneath a spray head 56 which applies a light spray of neutralizing liquid such as dilute acetic acid solution to the sheet, and then under a Weir trough 58 which floods water on the sheet to wash out the neutralizing acid. A trough 60 collects the acid and wash water draining from the sheet through the screen, from which trough a drain pipe 62 may lead to an acid recovery system (not shown), or to waste. A suction box 64 is provided at the front end of trough 60 to complete the removal of wash water and acid.

As it emerges from the caustic bath the fiber sheet is extremely limp and weak, so that the mere back drag of its own weight, if it were attempted to lift or pull it from the bath, would either cause it to disintegrate or to stretch so extensively that the useful felting effects of the caustic treatment would be substantially reduced or even completely lost. By positively supporting and lifting the sheet out of the caustic in the manner herein illustrated, the full effects of the caustic treatment are preserved. Preferably, as shown, the wash water is flooded gently, that is, with low impact force, onto the sheet, since the impact of a heavy spray might be sufficient to break up the sleazy fiber mass.

However, upon completion of the washing and neutralizing steps, the fiber sheet has, due to removal of the caustic, become essentially set in its changed, felted condition and has gained substantially its full final wet strength. It may, therefore, be handled with less support and care in further treatment without danger of material permanent stretching and loss of felting effect.

From the last suction box 64, the sheet, in the arrangement of apparatus shown, passes off the conveyor between squeeze rolls 66 to drying apparatus which, as shown, comprises a series of heated rotary cans or drying drums 68 of conventional form. Other methods of drying may be employed, for example, by festooning the sheet in a heated chamber, or by passing between banks of infra-red lamps. Upon leaving the drying cans 68, that is, after the drying has been completed, the sheet is in its final felted form.

To illustrate further a suitable practice of the process and production of the felt products of the invention, the following example is given:

The webs of cotton fibers, mainly from inch to 1 inch long, from six cards, were superposed in parallel, forming a single sheet which was passed through cold rollers under a pressure of about pounds per inch width of the rollers. This lightly pressed sheet weighed 41.0 grams per square yard and was 0.117 inch thick measured under a load of one gram per square inch.

The density of this carded fiber sheet was about the solution by means of a moving screen, rinsed.

with water, acidified with acetic acid, again washed with Water, and dried.

The finished material sustained an area con,- traction of had a density of 6.0 pounds per cubic foot and a thickness of 0.121 inch under a load of 25 grams per square inch. The extension at break in the lengthwise direction was 107% and in the widthwise direction 131% under loads of 5.6 pounds and 1.2 pounds respectively per inch of width. Its permeability was 88 cubic feet of air per minute per square foot measured in a standard permeability testing apparatus (made in accordance with the Schiefer-Boyland design described in the Bureau of Standards Report, R. P. 1471) at standard temperature and humidity.

In making strength comparisons between felts of different thicknesses and densities I make use of what I term corrected load, which is the actual load at break (in pounds per inch of width of the sample tested) divided by the weight in pounds of one square yard of the felt. This corrected load takes into account differences in weight of the compared felts, in effect, giving the strength of a unit quantity or'weight of. cotton fiber in different felts.

In the foregoing example, the felt produced had a corrected load of 10.4 lbs. in the lengthwise direction and 2.3 lbs. in the widthwise direction.,

Within limits, the process is subject to con.- siderable variation to produce different degrees of felting action and products which differ somewhat in the extent to which they possess the characteristic properties of the felts of the invention. For example, as a general rule, other conditions being equal, increasing the temperature of the caustic tends to diminish the degree of felting as measured by area shrinkage.

A denser felt having less extensibility and porosity but greater strength can be produced by compressing the laminated card webs, prior to causticizing, under heavy pressure of the order of 1500-1800 pounds per inch of width of pressure rollers. By cross-laying the successive card webs so that their long axes are at approximately 90 angles to each other, a felt of more evenly balanced strength lengthwise and widthwise may be obtained.

In general, the felts of this invention which, as previously stated, will have sustained an area shrinkage of at least 40% in causticizing, have an extensibility of at least 30% in either dimension, and preferably at least 75% in one dimension. Their dry strength corresponds to a corrected load at break, computed as previously explained, of at least about 5.0 pounds in the lengthwise direction and at least 1.3 pounds in the widthwise direction, and their wet strength is approximately one-half their dry strength. They have a permeability of at least 15 and generally less than 200 cubic feet of air per minute per square foot per 0.1 inch of thickness as measured by the standard apparatus above referred to, and a density of at least 3.0 pounds per cubic foot.

While the products of this invention are prepared by chemically treating cotton fibers, and the novel characteristics of such products are mainly dependent for their structural integrity on the presence of such fibers, it is possible to prepare many useful articles in which the felted cotton fibers serve as the main structure in which other fibers, for example, cellulosic or noncellulosic, thermoplastic, natural or synthetic fibers, such as kapok, wool, silk, vinyon, nylon, and regenerated cellulose may be dispersed. For

convenience, all the products of this invention even though they contain other fibers with the cotton fibers are referred to herein as cotton products or cotton felts.

The felts of this invention have many advantageous uses. Because of the high extensibility, flexibility, and conformability of the felts, they are more readily moldable than woven fabrics and may be molded by pressure, suction, etc. to shapes of such great irregularity as to break a equal thickness of laminated woven fabrics attempted to be shaped to a similar extent. Their high absorbency and porosity make them well suited as a base for impregnation with resins and other binders as, for example, to form artificial leather,

.and they are superior to materials previously used has been a serious difficulty with prior base materials, such as the conventional paper or cotton wadding. Their high extensibility makes them especially suited for impregnation with binders such as the elastomeric resins, since they will stretch and return freely with the elastic binder without rupturing, forming a highly elastic material. They are also readily moldable to irregular shapes when impregnated with a moldable plastic binder.

The felts of the invention, although having many valuable properties similar to those of wool felts, have important advantages over wool felts. For example, unlike wool felts, these felts can be Wetted without risk of causing further appreciable shrinkage and have pronounced resistance to alkalies and to high temperatures. They are more readily susceptible to dyeing. Furthermore, they donot contain proteins as do wool felts and, therefore, unlike the latter, are not attacked by moths and do not arouse allergic reactions. They are, therefore, particularly useful in clothing, for example, in shoulder pads, and in surgical dressings.

The extensibility of the feltmay, if desired, be reduced by laminating it with fabric or yarn, for example, by laminating an 18x 14 or 20 x 12 gauze between two pieces of the felt with a binder, such as latex. Such a laminated product has its extensibility restricted essentially to that of the gauze or other reinforcing material, but it retains substantially the extreme pliabilit and other properties of the felt alone. Also, if desired, the strength of the felt may be increased, although generally with reduced extensibility, softness and.

pliability, by added bonding agents which posi-' have an uneven, rough, crinkled surface, and

interferes with the permeability to fluids (liquid or gaseous), as well as other desirable physical characteristics of the finished, product.

While the process has been described and illustrated as. applied to the production of a continuous felt strip, it is not limited thereto- Thus,

, to 1 inch staple.

the process may be applied in similar manner to. the production of pieces of felt of an desired size and shape. The pieces may be solid or they may be tubular, or, for example, conical shaped hat bodies. Where tubular bodies are felted in a collapsed state, a piece of light, non-reactive material may be placed in the interior of the tube to prevent felting together of the opposite collapsed walls of the tube during causticizing, the nonreactive material offering no substantial resistance to the shrinkage of the tube While yet serving as a barrier between its walls. The fibrous material treated may be in the form of rope or roving of tangled fibers, formed, for example, b rolling.

' of a carded web. I

Individual pieces or bodies of the fiber may, for example, be felted by the use of apparatus such as illustrated herein by dropping the pieces in succession into a caustic bath, floatingthe pieces in the bath while they shrink and simultaneously carrying them along the tank by a current of causticwhich deposits them on an up wardly inclined conveyor screen, whereby they are carried out of the caustic and on which they are washed and acidified in like manner to the continuous strip.

In the practice of the invention, the cotton fibers employed are of textile length, that is, onehalf inch staple or more, and generally from I have found that the presence of such fibers at least in major proportion is essential to the manufacture of strong felts, in that shorter fibers do not develop sufficiently the. felting effects that are realized with the textile length fibers.

' I claim? 1. The method of felting cotton fibers of textile length to form a coherent unwoven textile material which comprises subjecting a body comprising said fibers intermingled in dry assembled sheet form to the action of a liquid causticizing agent for cellulose at low temperature while supporting said body by means of said liquid agent substantially without tensional stress and surface frictional restraint, thereby causing said fibers to intercurl, kink, and contract said body in area, and removing said causticizing agent from the fibers without substantially stretching said body, thereby fixing the fibers thereof in'said intercurled and kinked'condition and said body in area-contracted condition.

2; The method of felting cotton fibers of textile length to form a coherent unwoven textile mate-' rial which comprises subjecting a body compris ing said fibers intermingled in dry-assembled sheet form to the action of an aqueous NaOH solution of 8%-30% concentration and at a'tem-' perature between its freezing point and 25 C. while supporting said body by means of said solution substantially without tensional stress" and surface frictional restraint, thereby causing said fibers to intercurl, kink, and contract said bodyin area, and removing the NaOI-I from the fibers without substantially stretching said body,

thereby fixing the fibers thereof in said inter curled and kinked condition and said body'ini perature while continuously advancing'said strip said liquid agent substantially without-ten i3 sional stress and surface frictional restraint, thereby causing said fibers 'to intercurl, kink, and

contract said body in area, and thereafter con- 1 tinuously moving said body at a lesser linear rate than said feeding and removing said causticizing agent from the fibers without substantially stretching said body-thereby fixing the fibers thereof in said intercurled and kinked condition and said body in area-contracted condition.

4. The method of felting cotton fibers of textile length to 'form a coherent unwovenv textile material which comprises continuously feeding and subjecting a sheeted body comprising said fibers intermingled in dry-assembled strip form to a liquid causticizing agent for cellulose at low temperature while supporting'fsaid body substantially without tensional stress and surface frictional restraint in a forwardly moving stream of said liquid agent, thereby causing said fibers to intercurl, kink, and contract said body in area, separating the body from said stream at a lesser linear rate than said feeding and removing said causticizing agent from the fibers without substantially stretching said body, thereby fixing the fibers thereof in said intercurled and kinked condition and said body in area-contracted condition.

5. The method of felting cotton fibers of textile length to form a coherent unwoven textile material which comprises continuously feeding and subjecting a sheeted body comprising said fibers intermingled in dry-assembled strip form to a liquid causticizing agent for cellulose at low temperature while supporting said body substantially without tensional stress and surface frictional restraint in a forwardly moving but decelerating stream of said liquid agent, thereby causing said fibers to intercurl, kink, and contract said body in area, separating the body from said stream at a lesser linear rate than said feeding and removing said causticizing agent from the fibers without substantially stretching said body,

twists, bends and curls,'whereby the fibers are held together to form a conformable extensible coherent cotton felt, said felt having an extension of at least in at leastone dimension, and having a longitudinal corrected strength of at least 5 pounds.

9. Asan article of manufacture, an unwoven fabric of intermingled unspun fibers comprising essentially, and primarily dependent for its integrity upon, frictionally interlocked cotton fibers of textile length, said cottonfibers being characterized by artificially-induced irregular kinks, twists, bends and curls, whereby the fibers are held together to form a conformable extensible coherent cotton felt, said felt having an extension of at least 30% in at least one dimension and having a wet strength of approximately onehalf of its dry strength;

10. As an article of manufacture, an unwoven fabric of intermingled unspun fibers comprising essentially, and primarily dependent for its integrity upon, frictionally interlocked cotton fibers of textile length, said cotton fibers being characterized by artificially-induced irregular kinks, twists, bends and curls, whereby the fibers are held together to form a conformable extensible coherent cotton felt, said felt having an extension of at least 30% in at least one dimension and having other fibers dispersed therein.

thereby fixing the fibers thereof in said intercurled and kinked condition and said body in area-contracted condition.

mension.

'7. As an article-of manufacture, an unwoven fabric of intermingled unspun fibers comprising essentially, and primarily dependent for its integrity upon, frictionally interlocked cotton fibers of textile length, said cotton fibers being of shortened span and characterized by artificially-induced irregular kinks, twists, bends and curls, whereby the fibers are held together to form a conformable extensible coherent cotton felt, said irregular kinks, twists, bends and curls reducing the collective span of fibers by at least 40% and said felt having an extension of at least 30% in at least one dimension 8. As an article of manufacture, an unwoven fabric of intermingled unspun fibers comprising essentially, and primarily dependent for its integrity upon, frictionally interlocked cotton fibers of textile length, said cotton fibers being characterized by artificially-induced irregular kinks,

11. The. method of felting cotton fibers of textile length after boiling and bleaching to form a coherent unwoven textile material which comprises subjecting a body comprising said fibers intermingled in dry-assembled sheet form to the action of a liquid causticizing agent for cellulose at low temperature while supporting said body by means of said liquid agent substantiall without tensionalstress and surface frictional restraint, thereby causing said fibers to intercurl, kink, and contract said body in area, and removing said causticizing'agent from the fibers without substantially stretching said body, thereby fixing the fibers thereof in said intercurled and kinked condition and said body in area-contracted condition.

12. As an article of manufacture, an unwoven fabric of intermingled unspun fibers comprising essentially, and primarily dependent for its integrity upon, frictionally interlocked boiled and bleached cotton fibers of textile length, said cotton fibers being characterized by artificially-induced irregular kinks, twists, bends and curls, whereby the fibers are held together to form a conformable extensible coherent cotton felt, said felt having an extension of at least thirty percent in at least one dimension.

13. The method of felting cotton fibers of textile length after cleaning to form a coherent unwoven textile material which comprises subjecting a body comprising said fibers intermingled in dry-assembled sheet form to the action of a liquid causticizing agent for cellulose at low-temperature while supporting said body by means of said liquid agent substantially without tensional stress and surface frictional restraint, thereby causing'said fibers to intercurl, kink, and contract said body in area, and removing said causticizing agent from the fibers without substantially stretching said body, thereby fixing the fibers thereof in said intercurled and kinked condition and said body in area-contracted condition.

14. As an article of manufacture, an unwoven fabric of intermingled unspun fibers comprising essentially, and primarily dependent for its integrity upon, frictionally interlocked cleaned cotton characterized by artificially-induced irregular kinks, .twists, bends and curls, whereby the fibers are held together tolform a conformable extensible coherent cotton felt, said felt having an eX- tension of at least thirty percent in at least one dimension. I, HORACE A. SECRIST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Clapp Sept. 10, 1912 Number 15 Number I Name Date Melliand 1 June 18, 192-9 Schwartz May 6, 1930 Schwartz May 6, 1930 Schwartz 1 Feb. 3, 1931 Hanhart Mar. 3, 1931 Ahmert June 7, 1932 Leppin June13, 1933 Wilson Dec. 15, 1936 Novak et a1. June 15, 1937 Kleine 1 May 2, 1939 Mann Dec. 23, 1941 Andrews Mar. 17, 1942 FOREIGN PATENTS Country Date Great Britain Feb. 20, 1884 

1. THE METHOD OF FELTING COTTON FIBERS OF TEXTITLE LENGTH TO FROM A COHERENT UNWOVEN TEXTILE MATERIAL WHICH COMPRISES SUBJECTING A BODY COMPRISING SAID FIBERS INTERMINGLED IN DRY-ASSEMBLED SHEET FORM TO THE ACTION OF A LIQUID CAUSTICIZING AGENT FOR CELLULOSE AT LOW TEMPERATURE WHILE SUPPORTING SAID BODY BY MEANS OF SAID LIQUID AGENT SUBSTANTIALLY WITHOUT TENSIONAL STRESS AND SURFACE FRICTIONAL RESTRAINT, THEREBY CAUSING SAID FIBERS TO INTERCURL, KINK, AND CONTRACT SAID BODY IN AREA, AND REMOVING SAID CAUSTICIZING AGENT FROM THE FIBERS WITHOUT SUBSTANTIALLY STRETCHING SAID BODY, THEREBY FIXING THE FIBERS THEREOF IN SAID INTERCURLED AND KINKED CONDITION AND SAID BODY IN AREA-CONTRACTED CONDITION. 